class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None

class Solution:
    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
        if l1==None:return l2
        elif l2==None:return l1
        elif l1.val>=l2.val:
            l2.next=self.mergeTwoLists(l1,l2.next)
            return l2
        else:
            l1.next=self.mergeTwoLists(l1.next,l2)
            return l1